As television moves from an analog system to a digital system, several problems arise.
When the input image size and the display size are different, a resample processing which creates the pixel at a non-lattice position is needed. Also, in order to display interlaced video signals on a progressive display with high visual quality, it is necessary to ‘de-interlace’ interlaced odd and even fields of video signals into a sequentially continuous field of pixels without (inter-line) gaps.
Specifically, the most common method of implementing the interpolation function is to use a 2-line memory and generate the interpolated pixels from the pixel above (previous line) and the pixel below (next line). This implementation can be improved by using more lines to implement a higher order interpolation filter, giving slightly smoother images. However, those filters always operate on the basis that the current pixel is related to the pixel above and below it, which is completely untrue of edges with small angle. Whenever an edge is not vertical, the current pixel is related to those above and below it along the direction of the edge, e.g. if the angle is 45 degree the relationship is one up and one across and one down and one across. With small angle becomes more complex and will involve non-integer relationships. Moreover, currently prior art approaches only implement a simple angle interpolation; nothing is done on small angle edges.